Liquid crystal display device

ABSTRACT

Disclosed is a liquid crystal display device ( 700 ) capable of improving a display characteristic and a viewing angle as well as visibility in a reflection mode. A semi-transmissive film ( 600 ) is positioned between a light generating section ( 100 ) and a liquid crystal display panel ( 200 ) in order to partially transmit or reflect light supplied from an exterior. A polarizing plate ( 400 ), one surface of which is anti-glare treated, is positioned between the liquid crystal display panel ( 200 ) and the semi-transmissive film ( 600 ). The polarizing plate ( 400 ) diffuses light transmitted through or reflected from the semi-transmissive film. The display characteristic and viewing angle of the liquid crystal display device may be improved and reflectivity of light in the reflection mode may increase, so that visibility is improved.

TECHNICAL FIELD

The present invention relates to a liquid crystal display device, andmore particularly to a liquid crystal display device capable ofimproving a display characteristic and a viewing angle as well asvisibility in a reflection mode.

BACKGROUND ART

An electronic display device plays an important role in this age of aninformation-oriented society, and various kinds of electronic displaydevices are widely used in various industrial fields.

As a semiconductor technique makes great strides, solidification ofvarious electronic devices with low driving voltage, low powerconsumption, light weight and compact size has been achieved. In thisregard, there is required to fabricate a slimmer and lighter flat-paneltype display device having low driving voltage and low power consumptionadapted for new industrial environment.

Among presently developed display devices, a liquid crystal displaydevice has a slimmer and lighter structure with low power consumptionand low driving voltage, so it is widely used in various electronicappliances.

The liquid crystal display device is classified into a transmissive typeliquid crystal display device, a reflective type liquid crystal displaydevice and a reflective-transmissive type liquid crystal display devicedepending on a light source as used. The transmissive type liquidcrystal display device displays an image by using a light generatingsection positioned at a rear portion of a liquid crystal cell and thereflective type liquid crystal display device displays an image by usingnatural light. In addition, the reflective-transmissive type liquidcrystal display device uses a light source accommodated in a displaydevice when displaying an image in a room or in a place where anexternal light source is not provided (transmissive mode). If externallight is sufficiently provided, the reflective-transmissive type liquidcrystal display device displays an image by reflecting light incidentfrom the external light source (reflective mode).

The reflective-transmissive liquid crystal display device includes aliquid crystal display panel having a first substrate, a secondsubstrate opposite to the first substrate and a liquid crystal layerinterposed between the first and second substrates, and a lightgenerating section positioned at a rear portion of the liquid crystaldisplay panel.

The first substrate includes a transparent electrode and a reflectionelectrode connected to a thin film transistor (hereinafter, referred toTFT). Light radiated into the first substrate from the light generatingsection passes through the transparent electrode. The reflectionelectrode reflects light incident through the second substrate. That is,a transmissive region only exists in the transparent electrode. Theother parts of the first substrate act as a reflection region forreflecting light incident through the second substrate.

In addition, the second substrate includes a color filter consisting ofRGB pixels, which generate predetermined colors when light passestherethrough, an intercepting layer for preventing light from beingleaked between pixels, and a common electrode.

In addition, first and second polarizing plates are attached to outerportions of the first and second substrates, respectively, in order toallow external light to constantly pass through the first and secondsubstrates depending on an aligning direction of the liquid crystallayer. The first and second polarizing plates are arranged, such thatpolarizing axes thereof are vertically positioned to each other.

A first ¼λ, phase-difference plate is disposed between the firstsubstrate and the first polarizing plate, and a second ¼λ,phase-difference plate is disposed between the second substrate and thesecond polarizing plate. The first and second ¼λ phase-difference plateschange linear polarized light into circular polarized light or viceversa by applying a phase difference of ¼λ to two polarizing components,which are parallel to optical axes of the first and second ¼λphase-difference plates and vertical to each other.

However, according to the conventional reflective-transmissive typeliquid crystal display device, there is required to attach a broadband¼λ phase-difference plate to the first and second substrate,respectively, to cover the polarizing plate as well as a visible rayarea, so manufacturing cost thereof increases as compared with that ofthe transmissive type liquid crystal display device. In addition, lighttransmittance of the conventional reflective-transmissive type liquidcrystal display device is lower than that of the transmissive typeliquid crystal display device in the transmissive mode so the contrastratio (C/R) thereof will be lowered.

Furthermore, Δnd of the liquid crystal layer in the conventionalreflective-transmissive type liquid crystal display device is smallerthan and of the liquid crystal layer in the transmissive type liquidcrystal display device, so there is required to reduce a gap (d) of theliquid crystal cell and a refractive-index anisotropy (Δn) of liquidcrystal. Accordingly, not only is the manufacturing process of theconventional reflective-transmissive type liquid crystal display devicedifficult, but also the reliability of liquid crystal is lowered.

For this reason, a recently used reflective-transmissive type liquidcrystal display device adopts a structure capable of reflecting ortransmitting light from an exterior of the liquid panel while using theliquid crystal display panel of the transmissive type liquid crystaldisplay device. That is, the recently used reflective-transmissive typeliquid crystal display device includes a semi-transmissive sheet, whichallows a part of light incident between the liquid crystal display paneland the light generating section to transmit therethrough and reflectsthe remaining part of light.

However, the above structure represents inferior visibility and frontreflection characteristic in the reflective mode. That is, in thereflective mode, light incident through the first substrate isspecularly reflected at the semi-transmissive sheet, so visibility oflight is deteriorated and the viewing angle thereof becomes narrow.

DISCLOSURE OF THE INVENTION

The present invention provides a liquid crystal display device capableof improving a display characteristic and a viewing angle as well asvisibility in a reflection mode.

In one aspect of the invention, there is provided a liquid crystaldisplay device comprising: a light generating section to generate firstlight; a polarizing member disposed on the light generating section soas to generate third light by polarizing and diffusing first light; anda liquid crystal display panel disposed on the polarizing member todisplay an image by using third light and including a first substrate, asecond substrate opposite to the first substrate and liquid crystalinterposed between the first and second substrates.

In another aspect, there is provided a liquid crystal display devicecomprising: a light generating section to generate first light; asemi-transmissive film disposed on the light generating section in orderto allow first light to pass therethrough and to partially reflectsecond light directed in opposition to first light; a polarizing memberdisposed on the semi-transmissive film so as to generate fifth light bypolarizing and diffusing first light and to generate sixth light bypolarizing and diffusing second light; and a liquid crystal displaypanel disposed on the polarizing member to display an image byselectively receiving fifth light or sixth light and including a firstsubstrate, a second substrate opposite to the first substrate and liquidcrystal interposed between the first and second substrates.

According to the liquid crystal display device of the present invention,the semi-transmissive film is positioned between the light generatingsection and the liquid crystal display panel in order to partiallytransmit or reflect light supplied from an exterior light source. Inaddition, the polarizing plate, one surface of which is anti-glaretreated, is positioned between the liquid crystal display panel and thesemi-transmissive film. Thus, the display characteristic and viewingangle of the liquid crystal display device may be improved, andreflectivity of light in the reflection mode may be increased, so thatvisibility is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will becomereadily apparent by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a sectional view showing a transmissive type liquid crystaldisplay device according to one embodiment of the present invention;

FIG. 2 is a sectional view showing a reflective-transmissive type liquidcrystal display device according to one embodiment of the presentinvention;

FIG. 3 is a detailed view of a liquid crystal display panel shown inFIG. 2;

FIG. 4 is a detailed view of a semi-transmissive film shown in FIG. 2;

FIG. 5 is a detailed view of a polarizing member shown in FIG. 2;

FIG. 6 is a sectional view showing a polarizing member used in areflective-transmissive type liquid crystal display device according toanother embodiment of the present invention;

FIGS. 7A and 7B are views for illustrating an operation principle of areflective mode in a reflective-transmissive type liquid crystal displaydevice shown in FIG. 2; and

FIGS. 8A and 8B are views for illustrating an operation principle of atransmissive mode in a reflective-transmissive type liquid crystaldisplay device shown in FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a sectional view showing a transmissive type liquid crystaldisplay device 500 according to one embodiment of the present invention.

Referring to FIG. 1, the transmissive type liquid crystal display device500 of the present invention includes a light generating section 100, aliquid crystal display panel 200, a first polarizing plate 300 and asecond polarizing plate 400.

The light generating section 100 generates first light L1. The lightgenerating section 100 is aligned at a rear portion of the liquidcrystal display panel 200 in order to radiate first light L1 towards theliquid crystal display panel 200.

The liquid crystal display panel 200 includes a first substrate 210, asecond substrate 220 opposite to the first substrate 210 and a liquidcrystal layer 230 interposed between the first and second substrates 210and 220.

As shown in FIG. 3, the first substrate 210 includes a first glasssubstrate 211. A TFT 212 that acts a switching device and a transparentelectrode 213 comprised of conducive oxide layer, for example, such asindium-tin-oxide (hereinafter, referred to ITO), are formed on the firstglass substrate 211. In addition, the second substrate 220 includes asecond glass substrate 221. A color filter 222 including RGB colorpixels, an intercepting layer 223 for preventing light from being leakedbetween pixels, and a common electrode 224 comprised of ITO and disposedon the color filter 222 and the intercepting layer 223 are formed on thesecond glass substrate 221. The first and second substrates 210 and 220are arranged such that the transparent electrode 213 faces the commonelectrode 224.

The liquid crystal layer 230 is formed by using twisted nematic (TN)liquid crystal composition, which is twisted at a right angle.

The first and second polarizing plates 300 and 400 allow light toconstantly pass through the first and second substrates depending on analigning direction of the liquid crystal layer 230. In detail, the firstpolarizing plate 300 opposite to the second substrate 220 is disposed onan upper surface of the liquid crystal display panel 200 and the secondpolarizing plate 400 opposite to the first substrate 210 is disposed ona lower surface of the liquid crystal display panel 200. The first andsecond polarizing plates 300 and 400 absorb a part of polarizingcomponents of light and allow remaining polarizing components of lightto transmit therethrough, thereby constantly maintaining a transmittingdirection of light. The first and second polarizing plates 300 and 400are arranged such that polarizing axes thereof are vertical to eachother.

The second polarizing plate 400 includes a polarizing layer 410 and alight-diffusing layer 420. The light-diffusing layer 420 faces the lightgenerating section 100 and diffuses first light L1 so as to generatesecond light L2. The polarizing layer 410 is disposed on thelight-diffusing layer 420 in opposition to the first substrate 210. Thepolarizing layer 410 polarizes second light L2 in order to generatethird light L3. The light-diffusing layer 420 has a haze value above20%.

As shown in FIG. 5, the light-diffusing layer 420 includes a coatingmember 421 coated on one side of the polarizing layer 410 and ascattering member 422 mixed with the coating member 421. The coatingmember 421 is comprised of acryl-based resin and the scattering member422 is comprised of silica particles.

Therefore, first light L1 radiated from the light generating section 100is polarized and diffused by means of the second polarizing plate 400disposed between the liquid crystal display panel 200 and the lightgenerating section 100 before it is supplied to the liquid crystaldisplay panel 200. That is, the light-diffusing layer 420 of the secondpolarizing plate 400 diffuses first light L1 so as to generate secondlight L2, and the polarizing layer 410 polarizes second light L2 inorder to generate third light L3.

Then, third light L3 incident into the liquid crystal display panel 200passes through the liquid crystal layer 230, so that fourth light L4including image information is generated. Thus, the transmissive typeliquid crystal display device 500 is operated. In this case, the viewingangle of the transmissive type liquid crystal display device 500 may beimproved.

The second polarizing plate 400 may include the light-diffusing layer420 opposite to the first substrate 210 and the polarizing layer 410opposite to the light generating section 100. In this case, first lightL1 radiated from the light generating section 100 is polarized throughthe polarizing layer 410 and diffused by means of the light-diffusinglayer 420. The second polarizing plate 400 polarizes first light L1 byusing the polarizing layer 410 and diffuses first light L1 by using thelight-diffusing layer 420, thereby generating third light L3.

FIG. 2 is a sectional view showing a reflective-transmissive type liquidcrystal display device 700 according to another embodiment of thepresent invention. FIG. 3 is a detailed view of a liquid crystal displaypanel shown in FIG. 2.

Referring to FIG. 2, the reflective-transmissive type liquid crystaldisplay device 700 includes a light generating section 100, a liquidcrystal display panel 200, a semi-transmissive film 600, a firstpolarizing plate 300 and a second polarizing plate 400.

The light generating section 100 generates first light L1. The lightgenerating section 100 is disposed at a rear portion of the liquidcrystal display panel 200 in order to radiate first light L1 towards theliquid crystal display panel 200.

The liquid crystal display panel 200 includes a first substrate 210, asecond substrate 220 opposite to the first substrate 210, and a liquidcrystal layer 230 interposed between the first and second substrates 210and 220.

As shown in FIG. 3, the first substrate 210 includes a first glasssubstrate 211 on which a TFT 212 and a transparent electrode 213including ITO are formed at an upper surface thereof. The secondsubstrate 220 includes a second glass substrate 221. A color filter 222including RGB color pixels, an intercepting layer 223 for preventinglight from being leaked between pixels, and a common electrode 224including ITO and disposed on the color filter 222 and the interceptinglayer 223 are formed on the second glass substrate 221. The first andsecond substrates 210 and 220 are arranged such that the transparentelectrode 213 faces the common electrode 224.

The liquid crystal layer 230 is formed by using twisted nematic (TN)liquid crystal composition, which is twisted at a right angle.

FIG. 4 is a detailed view of the semi-transmissive film 600 shown inFIG. 2.

Referring to FIGS. 2 and 4, the semi-transmissive film 600 is disposedbetween the light generating section 100 and the liquid crystal displaypanel 200. The semi-transmissive film 600 includes two transparent filmshaving a refractive index different from each other. That is, a firstlayer 610 and a second layer 620 are alternately stacked on thesemi-transmissive film 600. The semi-transmissive film 600 reflects apart of incident light and allows the remaining of incident light totransmit therethrough.

On the assumption that a vertical direction of the semi-transmissivefilm 600 is a z-direction and a lateral surface of the semi-transmissivefilm 600 is an x-y surface, the first layer 610 has a refractive-indexanisotropy in the x-y surface thereof, and the second layer 620 has norefractive-index anisotropy in the x-y surface thereof. Accordingly, thesemi-transmissive film 600 has an anisotropic characteristic, whichrepresents that transmittance and refractive index of thesemi-transmissive film 600 are differently formed depending on thepolarizing state and direction of incident light.

If the refractive index of the first and second layers 610 and 620 issame to each other in the x and z-directions and different from eachother in the y-direction, when non-polarized light is incident in thevertical direction (z-direction) of the semi-transmissive film 600,polarizing components of the x-direction pass through thesemi-transmissive film 600 and polarizing component of the y-directionis reflected from the semi-transmissive film 600 according to Fresnel'sequation. An example of a birefringent dielectric multi-layer having theabove characteristic is a DBEF (dual brightness enhancement film)available from 3M company.

The DBEF has a multi-layered structure, in which two thin films made ofdifferent material are alternately stacked in hundreds of layers. Thatis, a polyethylene naphthalate layer having a high birefringence and apolymethyl methacrylate (PMMA) layer having an isotropic structure arealternately stacked one upon another, thereby forming the DBEF.Naphthalene radical has a planar structure, so the polyethylenenaphthalate layer is easily stacked to each other. The refractive indexin the stacking direction of the polyethylene naphthalate layer isremarkably different from the refractive index in the other directions.On the contrary, PMMA, which is amorphous high-polymer, is isotropicallyaligned so the PMMA layer has the same refractive index in alldirections thereof.

As described above, the DBEF of 3M company allows polarizing componentsof the x-direction to transmit therethrough and reflects polarizingcomponents of the y-direction. The x-direction is parallel to the firstpolarizing plate 300 and the y-direction is parallel to the secondpolarizing plate 400.

Referring again to FIG. 2, the first polarizing plate 300 opposite tothe second substrate 220 is disposed on an upper surface of the liquidcrystal display panel 200, and the second polarizing plate 400 oppositeto the first substrate 210 is disposed between the semi-transmissivefilm 600 and the liquid crystal display panel 200. The first and secondpolarizing plates 300 and 400 absorb a part of polarizing components oflight and allow remaining polarizing components of light to transmittherethrough, thereby constantly maintaining a transmitting direction oflight. The first and second polarizing plates 300 and 400 are arrangedsuch that polarizing axes thereof are vertical to each other.

FIG. 5 is a detailed view of the second polarizing plate 400 shown inFIG. 2.

Referring to FIGS. 2 and 5, the second polarizing plate 400 includes apolarizing layer 410 and a light-diffusing layer 420. Thelight-diffusing layer 420 faces the semi-transmissive film 600. Thelight-diffusing layer 420 diffuses first light L1 radiated from thelight generating section 100 so as to generate third light L3 in thetransmissive mode. Also, the light-diffusing layer 420 diffuses secondlight L2, which is natural light supplied from an exterior, in order togenerate fourth light L4 in the reflective mode. The polarizing layer410 is disposed on the light-diffusing layer 420 in opposition to thefirst substrate 210. The polarizing layer 410 polarizes third light L3and fourth light L4 in order to generate fifth light L5 and sixth lightL6, respectively. The light-diffusing layer 420 has a haze value above20%.

The light-diffusing layer 420 is formed through performing an anti-glare(AG) treatment with respect to one surface of the polarizing layer 410.In detail, the light-diffusing layer 420 includes a coating member 421and a scattering member 422 mixed with the coating member 421. Thecoating member 421 is comprised of acryl-based resin and the scatteringmember 422 is comprised of silica particles.

FIG. 6 is a sectional view showing a second polarizing plate 400 used ina reflective-transmissive type liquid crystal display device accordingto another embodiment of the present invention.

Referring to FIG. 6, the second polarizing plate 400 includes thelight-diffusing layer 420 opposite to the first substrate 210 and thepolarizing layer 410 opposite to the semi-transmissive film 600. In thetransmissive mode, the second polarizing plate 400 polarizes first lightL1 radiated from the light generating section 100 by means of thepolarizing layer 410 and diffuses first light L1 by means of thelight-diffusing layer 420, thereby supplying first light L1 to theliquid crystal display panel 200. In the reflective mode, the secondpolarizing plate 400 polarizes second light L2 supplied from theexterior by means of the polarizing layer 410 and diffuses second lightthrough the light-diffusing layer 420, thereby supplying second light L2to the liquid crystal display panel 200.

Referring again to FIG. 2, the reflective-transmissive type liquidcrystal display device 700 includes a transmitted light route T and areflected light route R. The transmitted light route T outputs firstlight L1 by way of the second polarizing plate 400, the liquid crystaldisplay panel 200 and the first polarizing plate 300 after transmittingfirst light L, which is forwarded to the first substrate 210 from thelight generating section 100, through the semi-transmissive film 600. Inaddition, the reflected light route R receives second light L2 from theexterior through the first substrate 210 and outputs second light L2 byway of the second polarizing plate 400, the liquid crystal display panel200 and the first polarizing plate 300 after reflecting second light L2at the semi-transmissive film 600.

In detail, first light L1 passing through the liquid crystal displaypanel 200 is partially reflected from the semi-transmissive film 600 inthe reflected light route R. First light L1 is polarized and diffused bymeans of the second polarizing plate 400 disposed between the liquidcrystal display panel 200 and the semi-transmissive film 600 beforefirst light L1 is again incident into the liquid crystal display panel200. That is, the light-diffusing layer 420 of the second polarizingplate 400 diffuses first light L1, which is specularly-reflected fromthe semi-transmissive film 600 so that it has a narrow viewing angle,thereby generating fourth light L4 having an improved viewing angle.Then, fourth light L4 is incident into the polarizing layer 410 of thesecond polarizing plate 420. Fourth light L4 is polarized by means ofthe polarizing layer 410, so that sixth light L6 is generated.

Then, sixth light L6 is incident into the liquid crystal display panel200 and passes through the liquid crystal layer 230. While passingthrough the liquid crystal layer 230, the polarizing state of sixthlight L6 is varied, so that eighth light L8 is generated. Eighth lightL8 is incident into the first polarizing plate 300 and polarized bymeans of the first polarizing plate 300, thereby generating tenth lightL10. Thus, the reflective-transmissive type liquid crystal displaydevice 700 is operated in the reflective mode. Thereflective-transmissive type liquid crystal display device 700 mayimprove reflectivity of light in the reflective mode, thereby improvingthe visibility and viewing angle of light.

In the transmitted light route T, first light L1 radiated from the lightgenerating section 100 is supplied into the liquid crystal display panel200 while passing through the semi-transmissive film 600. First light L1is polarized and diffused by means of the second polarizing plate 400disposed between the liquid crystal display panel 200 and thesemi-transmissive film 600 before it is supplied into the liquid crystaldisplay panel 200. That is, the light-diffusing layer 420 of the secondpolarizing plate 200 diffuses first light L1, thereby generating thirdlight L3 having an improved viewing angle, and the polarizing layer 410polarizes third light L3, thereby generating fifth light L5.

Then, fifth light L5 is incident into the liquid crystal display panel200. The polarizing state of fifth light L5 is varied by means of theliquid crystal display panel 200, so that seventh light L7 is generated.Seventh light L7 is polarized by means of the first polarizing plate300, so that ninth light L9 is generated. Thus, thereflective-transmissive type liquid crystal display device 700 isoperated in the transmissive mode. The reflective-transmissive typeliquid crystal display device 700 may improve the viewing angle of lightin the transmissive mode.

The light-diffusing layer 420 of the second polarizing plate 400prevents the Moiré phenomenon, which is created when a pattern of thesemi-transmissive film 600 is projected onto a screen of thereflective-transmissive type liquid crystal display device 700.

Hereinafter, an experimental example achieved by using thereflective-transmissive type liquid crystal display device 700 andcomparative examples 1 to 3 will be explained to compare the Moiréphenomenon, reflectivity, visibility, and viewing angle thereof witheach other.

In the experimental example, the reflective-transmissive type liquidcrystal display device 700 includes an anti-glare treated secondpolarizing plate 400 and a hard-coated first polarizing plate 300. Incomparative example 1, hard-coated first and second polarizing platesare used. In comparative example 2, an anti-glare treated firstpolarizing plate and a hard-coated second polarizing plate are used. Inaddition, anti-glare treated first and second polarizing plates are usedin comparative example 3.

Acryl-based resin mixed with silica particles is coated on thepolarizing plate through the anti-glare treatment, and acryl-based resinis coated on the polarizing plate through the hard-coating process.TABLE 1 1^(st) 2^(nd) polarizing polarizing Visibility Visibility plateplate Moiré Reflectivity (reflective (transmissive HC AG HC AGphenomenon (%) mode) mode) Comparative ◯ ◯ Strong 1.12 Normal Superiorexample 1 Comparative ◯ ◯ Weak 2.55 Inferior Superior example 2Comparative ◯ ◯ None 2.54 Inferior Superior example 3 Experimental ◯ ◯None 1.32 Superior Superior example

As shown in table 1, comparative example 1, in which the first andsecond polarizing plates are subject to hard-coating process withoutbeing subject to the anti-glare treatment, represents superiorvisibility in the transmissive mode. However, the Moiré phenomenon isstrongly represented in comparative example 1 as compared with those ofthe experimental example and comparative examples 2 and 3, in which oneof the first and second polarizing plates is anti-glare treated. Inaddition, reflectivity of comparative example 1 is lower than those ofthe experimental example and comparative examples 2 and 3, so normalvisibility is represented in the reflective mode.

Comparative example 2, in which the first polarizing plate is subject tothe anti-glare treatment and the second polarizing plate is subject tothe hard-coating process, represents the Moiré phenomenon weaker thanthat of comparative example 1 and superior visibility in thetransmissive mode. In addition, comparative example 2 representsreflectivity higher than that of comparative example 1. However,although reflectivity of comparative example 2 is higher than that ofcomparative example 1, reflectivity of comparative example 2 is derivedfrom light reflected from the first polarizing plate, which includeslight reflected before it passes through the liquid crystal layer.Accordingly, although reflectivity of comparative example 2 is higherthan those of comparative example 1 and the experimental example,comparative example 2 represents inferior visibility in the reflectivemode.

Comparative example 3, in which the first and second polarizing platesare subject to the anti-glare treatment, does not create the Moiréphenomenon, with representing superior visibility in the transmissivemode. Comparative example 3 represents reflectivity higher than that ofcomparative example 1. However, as the same as comparative example 2,reflectivity of comparative example 3 is derived from light reflectedfrom the first polarizing plate, which includes light reflected beforeit passes through the liquid crystal layer. Accordingly, althoughreflectivity of comparative example 3 is higher than those ofcomparative example 1 and the experimental example, comparative example3 represents inferior visibility in the reflective mode.

The experimental example, in which the first polarizing plate is subjectto the hard-coating process and the second polarizing plate isanti-glare treated, does not create the Moiré phenomenon withrepresenting superior visibility in the transmissive mode. In addition,the experimental example represents reflectivity higher than that ofcomparative example 1 and lower than those of comparative examples 2 and3. However, reflectivity of the experimental example is derived fromlight, which has transmitted through the liquid crystal layer therebyobtaining image information, so the experimental example representssuperior visibility in the reflective mode as compared with visibilityof comparative examples 2 and 3. Reflectivity of the experimentalexample increases as compared with reflectivity of comparative example 1about 18%, so the experimental example represents visibility superiorthan that of the comparative example 1 in the reflective mode.

Hereinafter, an operation principle of the reflective-transmissive typeliquid crystal display device 700 in the reflective mode and thetransmissive mode will be explained.

FIGS. 7A and 7B are views for illustrating the operation principle ofthe reflective mode in the reflective-transmissive type liquid crystaldisplay device.

Referring to FIG. 7A, when pixel voltage is applied to the liquidcrystal layer in the reflective mode, light supplied from the exterioris linearly polarized in parallel to a polarizing axis thereof bypassing through the first polarizing plate 300. Linearly polarized lightpasses through the liquid crystal layer 230 and the transparentelectrode 213 so that light is again linearly polarized in a directionvertical to the polarizing axis of the first polarizing plate 300 and isincident into the semi-transmissive film 600. The polarizing axis of thefirst polarizing plate 300 is vertical to the polarizing axis of thesecond polarizing plate 400, so light incident into the secondpolarizing plate 400 is parallel to the polarizing axis of the secondpolarizing plate 400. Accordingly, a part of light, which is linearlypolarized in parallel to the polarizing axis of the second polarizingplate 400 passes through the semi-transmissive film 600 and theremaining part of light is reflected from the semi-transmissive film600.

Linearly polarized light, which is specularly-reflected from thesemi-transmissive film 600, is diffused by means of the light-diffusinglayer 420 of the second polarizing plate 400 and linearly polarized bymeans of the polarizing layer 410, so that light having improved viewingangle is outputted. In addition, diffused and linearly polarized lightpasses through the transparent electrode and the liquid crystal layer230. Since the liquid crystal layer 230 is aligned depending on pixelvoltage applied thereto, the polarizing state of diffused and linearlypolarized light is varied while passing through the liquid crystal layer230. Therefore, light is linearly polarized in a direction parallel tothe polarizing axis of the first polarizing plate 230, and then passesthrough the first polarizing plate 300, thereby displaying a whiteimage.

As shown in FIG. 7B, when pixel voltage is not applied to the liquidcrystal layer in the reflective mode, light supplied from the exteriorpasses through the first polarizing plate 300 and is linearly polarizedin a direction parallel to the polarizing axis of the first polarizingplate 300. Since pixel voltage is not applied to the liquid crystallayer 230, linearly polarized light passes through the liquid crystallayer 230 without varying the polarizing state of linearly polarizedlight and is incident into the semi-transmissive film 600. Linearlypolarized light is selectively reflected from the semi-transmissive film600 or passes through the semi-transmissive film 600 so that light issupplied into the second polarizing plate 400. Light incident into thesecond polarizing plate 400 has a direction vertical to the polarizingaxis of the second polarizing plate 400, so it is absorbed in the secondpolarizing plate 400.

Therefore, light is not reflected from the semi-transmissive film 600,so a black image is displayed.

FIGS. 8A and 8B are views for illustrating the operation principle ofthe transmissive mode in the reflective-transmissive type liquid crystaldisplay device.

Referring to FIG. 8A, when pixel voltage is applied to the liquidcrystal layer in the transmissive mode, light supplied from the lightgenerating section 100 is incident into the semi-transmissive film 600.The semi-transmissive film 600 allows polarizing components parallel tothe x-axis direction, which are included in light parallel to thepolarizing axis of the second polarizing plate 400, to be partiallyreflected therefrom or to partially pass therethrough, and reflectspolarizing components, which are parallel to the y-axis direction.

Light passing through the second polarizing plate 400 by way of thesemi-transmissive film 600, is diffused by means of the diffusing layer420 of the second polarizing plate 400 so that the viewing angle oflight is improved. Then, light is linearly polarized in a directionparallel to the polarizing axis of the second polarizing plate 400 bymeans of the polarizing layer. That is, light is linearly polarized in adirection vertical to the polarizing axis of the first polarizing plate300. Then, diffused and linearly polarized light passes through thetransparent electrode 213 and the liquid crystal layer 230, so thatlight is again linearly polarized in a direction parallel to thepolarizing axis of the first polarizing plate 300. Since the liquidcrystal layer 230 is aligned in a predetermined pattern due to pixelvoltage applied thereto, the polarizing state of diffused and linearlypolarized light is adjusted by means of the liquid crystal layer 230.

Accordingly, light polarized in parallel to the polarizing axis of thefirst polarizing plate 300 by means of the liquid crystal layer 230passes through the first polarizing plate 300, thereby displaying awhite image.

As shown in FIG. 8B, when maximum pixel voltage is not applied to theliquid crystal layer in the transmissive mode, light radiated from thelight generating section 100 is incident into the semi-transmissive film600. The semi-transmissive film 600 allows a part of light to passtherethrough and reflects a remaining part of light Light passingthrough the second polarizing plate 400 by way of the semi-transmissivefilm 600 is diffused by means of light-diffusing layer 420, so that theviewing angle of light is improved. Then, light is linearly polarized ina direction parallel to the polarizing axis of the second polarizingplate 400 by means of the polarizing layer 410. That is, light islinearly polarized in a direction vertical to the polarizing axis of thefirst polarizing plate 300. Then, linearly polarized light having theimproved viewing angle passes through the transparent electrode 213 andthe liquid crystal layer 230 without varying the polarizing statethereof.

Therefore, light, which is linearly polarized in the direction verticalto the polarizing axis of the first polarizing plate 300 does not passthrough the first polarizing plate 300, so a black image is displayed.

According to the liquid crystal display device of the present invention,the semi-transmissive film is positioned between the light generatingsection and the liquid crystal display panel in order to partiallytransmit or reflect light supplied from the exterior. In addition, thepolarizing plate, one surface of which is subject to the anti-glaretreatment, is positioned between the liquid crystal display panel andthe semi-transmissive film.

Therefore, the viewing angle of the liquid crystal display device may beimproved and reflectivity of light may be increased in the reflectivemode, thereby improving visibility. In addition, the present inventionmay prevent the Moiré phenomenon, which is caused when a pattern of thesemi-transmissive film is projected onto a screen of thereflective-transmissive type liquid crystal display device.

While the present invention has been described in detail with referenceto the preferred embodiments thereof, it should be understood to thoseskilled in the art that various changes, substitutions and alterationscan be made hereto without departing from the scope of the invention asdefined by the appended claims.

1. A liquid crystal display device comprising: a light generatingsection to generate first light; a polarizing member disposed on thelight generating section so as to generate third light by polarizing anddiffusing first light; and a liquid crystal display panel disposed onthe polarizing member to display an image by using third light andincluding a first substrate, a second substrate opposite to the firstsubstrate and liquid crystal interposed between the first and secondsubstrates.
 2. The liquid crystal display device as claimed in claim 1,wherein the polarizing member comprises: a light-diffusing layerpositioned in opposition to the light generating section so as togenerate second light by diffusing first light; and a polarizing layerdisposed on the light-diffusing layer so as to generate third light bypolarizing second light.
 3. The liquid crystal display device as claimedin claim 1, wherein the polarizing member comprises: a polarizing layerpositioned in opposition to the light generating section so as togenerate second light by polarizing first light; and a light-diffusinglayer disposed on the polarizing layer so as to generate third light bydiffusing second light.
 4. A liquid crystal display device comprising: alight generating section to generate first light; a semi-transmissivefilm disposed on the light generating section in order to allow firstlight to pass therethrough and to partially reflect second lightdirected in opposition to first light; a polarizing member disposed onthe semi-transmissive film so as to generate fifth light by polarizingand diffusing first light and to generate sixth light by polarizing anddiffusing second light; and a liquid crystal display panel disposed onthe polarizing member to display an image by selectively receiving fifthlight or sixth light and including a first substrate, a second substrateopposite to the first substrate and liquid crystal interposed betweenthe first and second substrates.
 5. The liquid crystal display device asclaimed in claim 4, wherein the polarizing member comprises: alight-diffusing layer positioned in opposition to the semi-transmissivefilm so as to generate third light by diffusing first light and togenerate fourth light by diffusing second light; and a polarizing layerdisposed on the light-diffusing layer so as to generate fifth light bypolarizing third light and to generate sixth light by polarizing fourthlight.
 6. The liquid crystal display device as claimed in claim 5,wherein the light-diffusing layer has a haze value above 20%.
 7. Theliquid crystal display device as claimed in claim 5, wherein thelight-diffusing layer comprises coating material coated on one surfaceof the polarizing layer and scattering material mixed with coatingmaterial.
 8. The liquid crystal display device as claimed in claim 7,wherein coating material comprises acryl-based resin and scatteringmaterial includes silica particles.
 9. The liquid crystal display deviceas claimed in claim 4, wherein the polarizing member comprises: apolarizing layer positioned in opposition to the semi-transmissive filmso as to generate third light by polarizing first light and to generatefourth light by polarizing second light; and a light-diffusing layerdisposed on the polarizing layer in opposition to the first substrate soas to generate fifth light by diffusing third light and to generatesixth light by diffusing second light.
 10. The liquid crystal displaydevice as claimed in claim 4, wherein the second substrate comprises acolor filter and a first electrode and the first substrate comprises aswitching device and a second electrode opposite to the first electrode.